Mohamed Ibrahim Bassyouni
2020 / 4 / 28
While we watch the number of cases and deaths climb, experts also are closely eyeing what they call the case fatality rate (CFR). This tells the proportion of people who have been confirmed as having Covid-19 and ultimately die from the illness, and it’s a number that has been varying widely from country to country.
Some countries, such as Egypt it is 7.1, Germany, have a fatality rate of approximately 3 percent of confirmed cases, whereas Italy’s rate has climbed above 13 percent. Even within the US, large differences have emerged: As of April 20, Michigan had reported a CFR of 7.6 percent, compared to Oregon’s 3.8 percent.
Since scientists are pretty sure the virus isn’t mutating very quickly, the pathogen itself shouldn’t be more deadly in one place than another. So why the variation?
Figuring out what is driving these disparate numbers reveals differences not just in population demographics but also in health care capacity and government response. Understanding CFRs might also help us slow deaths around the world especially for the most vulnerable countries and individuals.
Why might fatality rates be so radically different?
Before diving into the details from different countries, it’s worth looking at some of the broad reasons why death rates can look so starkly different from place to place.
First, we know that there are big differences in the risk the virus poses to different age groups. For this coronavirus, SARS-CoV-2, older individuals are far more likely to become critically ill´-or-die from the disease. In a paper in The Lancet Infectious Diseases, researchers concluded, when looking at data from China and elsewhere, that people between the ages of 40 and 49 have an estimated CFR of about 0.4 percent-;- for those 80 and older, it’s 13.4 percent. This gulf of survivability is already playing out in some countries with older populations, such as Italy.
Additionally, Covid-19 has been demonstrably deadlier for those with existing health conditions, including lung disease (often caused by smoking), cardiovascular disease, severe obesity, diabetes, kidney failure, and liver disease. So countries´-or-regions with less healthy populations might also be seeing big differences in the rates at which people are dying from the illness.
Beyond the varying impacts of the illness itself, there are lots of variables in how numbers are being gathered and reported. Perhaps the biggest factor here is testing. When experts calculate a basic fatality rate, it can be as simple as dividing the number of deaths by the number of confirmed cases
Since the international spread of the novel coronavirus, countries have varied widely in their ability and willingness to roll out testing. So that means the denominator (the number of cases) can be closer´-or-further from an accurate count of how many people actually have the virus. The larger the percentage of a population that has been tested, the more complete picture we will get of the virus’s actual fatality rate there.
The other issue with the poor testing rates is sampling bias. Tests that are available are usually saved for the sickest and riskiest cases. This pushes the fatality rate higher than it actually is because the testing is more likely to omit mild´-or-asymptomatic cases and instead overrepresents those who are more likely to die. So, as testing becomes more widespread in various countries, their fatality rates will drop.
That is no reason for optimism, as the authors of the study in The Lancet note. The researchers offer an overall CFR for Covid-19 at 1.38 percent, which reflects their estimates for lack of testing and other factors, including potential censorship. This number, they noted, is still “substantially higher than for recent influenza pandemics (e.g. H1N1 influenza in 2009)” “swine flu” which had a case fatality rate of 0.1 percent. Their estimated CFR, “combined with likely infection attack rates (around 50-80 percent), shows that even the most advanced health-care systems are likely to become overwhelmed.” It is clear that this is far worse than the seasonal flu.
Another way to look at death rates in the absence of widespread testing is to compare the number of Covid-19 deaths to a country’s total population, which is what researchers have done.
In another effort to make up for incomplete testing (and possibly incomplete reporting), researchers are attempting to estimate what percentage of actual cases have been reported (as of a couple weeks ago) for each country.